Ryu sits next to 3 phonetic neighbors — Drew, Lew, and Rue are the closest matches by sound. Most share Ryu's Japanese cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"flow, current, stream"
"immortality, eternal life (symbolic)"
"spring, fertility (earlier meaning)"
"complete, whole"
"beloved (David) + valley (Devon)"
"generosity, nobility"
"life-giving"
"youth, young warrior"
"his peace, his wholeness"
"staff bearer, wand wielder"
"mountain"
"one who works with books"
"reminiscent of paladin (heroic knight)"
"cloud"
"growth, abundance, increase"
"flowing down (from Jordan)"
"strength"
"rejoicing, exultation"
"crooked nose (Cameron root)"
"follower of Dionysus, god of wine"
"jaybird + euphonic suffix"
Similar sound: These names share phonetic patterns with Ryu — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Japanese origins, giving them the same cultural heritage as Ryu.
Rhythm: Ryu is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.